Amazon has apologised for sending out some pre-ordered copies of The Testaments, Margaret Atwood's follow-up to The Handmaid's Tale.
The online retailer said "a technical error" had caused some US customers to be "inadvertently sent copies".
"We apologise for this error; we value our relationship with authors, agents, and publishers," said a statement.
They added that they regretted "the difficulties this has caused them and our fellow booksellers".
Publisher Penguin Random House had instructed sellers to keep the much-anticipated sequel strictly under wraps until its release on 10 September.
The lucky customers who wrongly received the book were overjoyed.
"I feel like I won the lottery!" said one.
"Wow!! A week early?!" wrote another.
blessed be The Testaments— Amy Cutlip (@amy_cutlip) September 3, 2019
(may the book open) pic.twitter.com/hhJx1rULDt
Penguin Random House would not confirm how many copies were sent, but The Guardian put the figure at 800.
In an earlier statement, Penguin Random House said: "In the US a very small number of copies of Margaret Atwood's The Testaments were distributed early due to a retailer error which has now been rectified.
"We appreciate that readers have been waiting patiently, in some cases for more than 30 years, for the much-anticipated sequel to the bestselling The Handmaid's Tale. In order to ensure our readers around the world receive their copies on the same day, our global publication date remains Tuesday 10 September."
The Testaments is the most eagerly-awaited title of the year, and comes 34 years after Atwood's original. It has already been shortlisted for The Booker Prize.
The error angered other retailers, who said they would be punished if they made the same mistake, and suspected Amazon would not face the same consequences.
The American Booksellers Association expressed its "strong disappointment regarding this flagrant violation of the agreed protocol in releasing this book to the public".
Lexi Beach, owner of New York's Astoria Bookshop, said she had to sign an embargo agreement promising that copies of the book would be "stored in a monitored and locked, secured area and not placed on the selling floor prior to the on-sale date".
The strict security measures included sending review copies to critics with a fake title and cover, according to the Washington Post's Ron Charles.
The reviews are in - 'A success', 'a giddy thrillride' and 'less devastating'
The Testaments is "an entirely different novel in form and tone" compared with its predecessor, Ron Charles wrote.
Aunt Lydia, one of the handmaids' matriarchal mentors, is one of three narrators in the new book - "a brilliant strategic move that turns the world of Gilead inside out", the Washington Post critic said.
He added: "The Testaments is not nearly the devastating satire of political and theological misogyny that The Handmaid's Tale is. In this new novel, Atwood is far more focused on creating a brisk thriller than she is on exploring the perversity of systemic repression."
The Guardian's Alex Clark said The Testaments was "a success that more than justifies her Booker Prize shortlisting", and "a rallying cry for activism", with brutality that is "still shocking".
It "takes us to a subtly altered Gilead and in many ways a more hopeful one", she wrote.
According to a review by The Telegraph's Serena Davies, which contains spoilers, the new book "has the dramatic thrust and power to shock to scorch the memory".
It is "a blockbuster of propulsive, almost breathless narrative, stacked with twists and turns worthy of a Gothic novel", she wrote.
In The New York Times's review, which also contains major spoilers, Michiko Kakutani wrote: "Atwood's sheer assurance as a storyteller makes for a fast, immersive narrative that's as propulsive as it is melodramatic."
The author's powers "are on full display", according to The Los Angeles Times' Susan Straight, while USA Today's Barbara VanDenburgh declared that The Testaments was "worthy of the literary classic it continues".
The book picks up 15 years after the end of the original, and the other two narrators are a young woman raised in a powerful Gilead family and the other from a 16-year-old Canadian girl.
Despite the darkness of the original, Slate and Vox both agreed that the follow-up was "fun to read".
"It's a romp. But that giddiness is also what makes The Testaments feel slighter than The Handmaid's Tale," wrote Vox's Constance Grady.
It has "a corker of a plot", according to Slate's Laura Miller, who noted that Atwood had been influenced by the TV series, which has gone beyond the plot of the original book. "Its tone hews closer to the series than to the novel that precedes it," she wrote.
The Hulu TV series, starring Elisabeth Moss, which airs on Channel 4 in the UK, has been renewed for a fourth season.
Hulu will also adapt The Testaments for the small screen, according to Time Magazine, but it's not yet clear whether Atwood's new story will be folded into the existing show or developed as a separate drama.